From Coordinated Universal Time on Wikipedia:
Coordinated Universal Time (UTC) is a time standard based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the Earth’s slowing rotation.
From Greenwich Mean Time on Wikipedia:
UTC is an atomic time scale which only approximates GMT with a tolerance of 0.9 second
One is measured from the sun and another from an atomic clock.
For your purposes, they are the same.
The practical difference is that if a system is set up to use UTC then it will not automatically switch to daylight savings time while if you set your time zone to GMT then there’s a good chance it automatically switches to BST during the summer without you noticing.
For computers, GMT is UTC+0 – so they are the equivalent.